Study On The Effect Of Melt Composite Treatment And Microstructure Regulation On Electrical And Mechanical Properties Of 6101 Aluminum Alloy

With the rapid development of electrical and electric,new energy electric vehicle industry,aluminum and aluminum alloy conductors,with the advantages of low density,high specific strength and stiffness,easy installation,and low price,gradually replace the current widely used copper and copper alloy conductors in the field of overhead transmission lines,showing broad application prospects for national sustainable development,efficient energy use,and accelerating the realization of the"double carbon"target.At present,in order to meet the comprehensive performance requirements of overhead transmission lines,more and more types of conductive aluminum alloys are being researched,among which 6101 aluminum alloy is one of the most commonly used conductive aluminum alloys.In this paper,6101 aluminum alloy is studied to optimize the alloy composition and improve the microstructure with the help of composition control,compound boronization treatment,hot extrusion deformation,and heat treatment to enhance its mechanical properties and electrical conductivity simultaneously.The main research contents and conclusions of this paper are as follows:（1）The effect of alloy composition on the electrical conductivity-mechanical properties of 6101 aluminum alloy.Using 6101 as a study subject,the best Mg,Si,and Fe additions in the range of 6101composition,along with heat treatment,were looked into to improve its electrical conductivity and mechanical properties at the same time.First,experiments combined with theoretical calculations determined two optimal Mg and Si additions:Al-0.7Mg-0.5Si and Al-0.4Mg-0.7Si,with conductivities of 51.5%IACS（international standard annealed copper）and 51.4%IACS,respectively,which were increased to 57.0%IACS and55.7%IACS after homogenization treatment.On this basis,considering the simultaneous optimization of conductivity and mechanical properties of the alloy,an appropriate amount of Fe was added and heat treatment was carried out.The results showed that for 6101aluminum alloy,the ideal Mg/Si mass ratio was 1.4,high Mg and low Si were beneficial to obtain good electrical conductivity and mechanical properties,and the alloy conductivity took longer to peak at a low Mg/Si mass ratio.Finally,by adjusting the Mg,Si,and Fe contents in 6101 aluminum alloy,an Al-0.7Mg-0.5Si-0.2Fe alloy was obtained,and its electrical conductivity could reach 56.3%IACS and 91.3 Hv after homogenization treatment.（2）The effect of melt compound treatment on the electrical conductivity of 6101aluminum alloy.Al-0.7Mg-0.5Si-0.2Fe was subjected to conventional boronization treatment and transition group metal element-assisted boronization treatment,and the mechanism of the effect of transition group metal elements（Zr,V,and Ti）on the composite boronization treatment was investigated in detail.The results showed that the electrical conductivity of Al-0.7Mg-0.5Si-0.2Fe increased and then decreased with the increase of B content,and reached a maximum of 53.4%IACS at a B addition of 0.09%（all compositions are wt.%in this paper unless otherwise stated）.By analyzing the precipitation layer of conventional boronization treatment,it was found that the boronization treatment product was doped Al B₂@TMB₂polyboride with core-shell structure,and the core was unreacted Al B₂,so the conventional boronization reaction was not sufficient and the boronization treatment efficiency was low.It was found that the electrical conductivity of Al-0.7Mg-0.5Si-0.2Fe reached 54.2%IACS,53.9%IACS,and 53.7%IACS when Zr,V,and Ti were added at0.05%,0.06%,and 0.03%,respectively.With the best Zr-assisted boronization treatment,the Al-0.7Mg-0.5Si-0.2Fe had an 8.2%increase in electrical conductivity compared to the untreated（50.1%IACS）.It was known from both thermodynamic and kinetic analyses that the trace amount of Zr was more favorable to promote the transition group metal element impurities in the melt to continue to fully react with the core Al B₂and break the core-shell structure,thus achieving efficient boronization and ultimately resulting in a significant increase in the electrical conductivity of Al-0.7Mg-0.5Si-0.2Fe.（3）Effects of hot extrusion and heat treatment on electrical conductivity-mechanical properties of Al-0.7Mg-0.5Si-0.2Fe alloyBased on the above study,the Al-0.7Mg-0.5Si-0.2Fe alloy was deformed and heat treated to investigate the effects of extrusion ratio and heat treatment on its microstructure and electrical conductivity-mechanical properties.It was found that the electrical conductivity of the alloy was 53.5%IACS and 52.0%IACS after hot extrusion at extrusion ratios of 36:1 and 100:1,respectively,and was slightly reduced compared with that of the as-cast alloy,due to the introduction of dislocations and deformation weaving by deformation.In order to achieve the simultaneous improvement of mechanical properties and electrical conductivity of the alloy,the above alloy was heat-treated and the optimal heat treatment process was investigated,and the results showed that:the ultimate tensile strength reached 282 MPa and the electrical conductivity was 59.1%IACS with an extrusion ratio of 100:1+540℃/2 h solid solution+240℃/12 h aging.The ultimate tensile strength was 254 MPa and the electrical conductivity was 61.1%IACS with an extrusion ratio of 100:1+540℃/2 h solid solution+240℃/16 h aging.the ultimate tensile strength was 268 MPa and the electrical conductivity was 60.1%IACS at 100:1+540°C/2 h solid solution+240°C/1 h+180°C/8 h double aging.The heat treatment eliminated the dislocations and other defects introduced by hot extrusion and caused the solid solution elements to precipitate and form the second phase.The second phase was formed,and the second phase particles were broken and refined with uniform distribution,which significantly improved the electrical conductivity and mechanical properties of 6101aluminum alloy,and provided a basis for the subsequent research on 6101 aluminum alloy.